Wherever quantitative fluorescence immunoassays; for example, are carried out, sample carriers are known that have a multiplicity of electrodes, for example 10,000 electrodes, to which an electric voltage can be applied selectively. If different sample liquids are led over the electrodes, different samples can be produced by deposition at the electrodes, depending on the application of specific voltages. Since these samples are marked by two or more fluorescence carriers, they luminesce differently in the case of excitation by different optical wavelengths. Biochemical properties can be measured in this way.
It is known in this connection to use dichroic, permanently installed mirrors in order to achieve a separation of the different fluorescence wavelengths that are emitted by the sample carrier. In this case, a problem exists in that dichroic mirrors can be operated typically only when the beam path is parallel to the position of the dichroic mirrors. In addition, such mirrors are not 100% efficient. At the same time, they also require the excitation sources to be electrically clocked.
Sample carriers produced using semiconductor technology are, for example, built up in several layers and have a multiplicity of cylindrical platinum electrodes to which it is possible to apply the abovementioned voltages. The sample carriers are arranged in plastic containers covered in each case with a glass layer, it being possible for the sample liquids to flow through the space between the glass layer and plastic container and come into contact in the process with electrodes.
Document DE 39 26 090 C2 discloses a dual-beam photometer in which a rotatable mirror system divided into silvered and transmitting sectors is used to split a light bundle issuing from a light source into a measuring beam and into a reference beam. The two beam paths are recombined by the same mirror system, the measuring beam penetrating the mirror system and passing through a sample to be examined, and the reference beam being reflected at the mirror system and therefore not impinging on the sample. The recombined beam is detected by a detector device. Consequently, the influence of fluctuations in the light source brightness or the detector sensitivity can be eliminated given suitable evaluation of the detected measuring signals. DE 39 26 090 C2 further discloses in accordance with an exemplary embodiment a dual-beam photometer having a second light source emitting a continuous spectrum (see FIG. 4), whose radiation is used in a fashion alternating with the first light source both as measuring beam and as a reference beam when a mirror system divided into four sectors (two silvered and two transparent sectors) is used. It is possible in this way additionally to achieve compensation of background radiation.